The overall objective of this work is to detail the mechanism of selective IgG transport across the small intestine of the neonatal rat. The system represents one of the best documented examples of receptor-mediated transport of a specific protein across cells. Studies which will be continued during the coming year include (a) evaluation of possible effects of transported immune complexes on the developing immune system, (b) characterization of receptor-IgG binding by a radioimmunoassay and (c) isolation of the membrane receptor by affinity chromatography.